Spark plug



A ril 25, 1939. H N 2,155,481

SPARK PLUG Filed April 1, 1938 I N V EN TOR. FduIHHHbMEIFL-I'HH gwaw A TTORNEY Patented Apr. 25, 1939 SPARK PLUG Edward Howell Fenn, West Hartford, Conn, as-

signor to United Aircraft Corporation, East Hartford, Conn, a corporation of Delaware Application April 1, 1938, Serial No. 199,477

Claims.

This invention relates to improvements in spark plugs and has for anobject the provision of an improved spark plug which may be readily disassembled for inspection and repair.

- parts so that a worn or damaged part may be economically replaced without requiring the replacement of a complete spark plug.

' Other objects and advantages will be more particularly pointed out hereinafter or will become apparent as the description proceeds.

In the accompanying drawing, in which like reference numerals are used to designate similar parts throughout, there is illustrated in two somewhat modified forms a suitable mechanical embodiment of what is now considered to be the preferred form of the invention. The drawing however, is for the purpose of illustration only and is not to be taken as limiting the scope of the invention as set forth in the appended claims.

In the drawing I ,Fig. 1 is a partly sectional view of one form of spark plug constructed according to themvention and also shows a fragmentary portion of acylinder head adapted to receive the spark plug.

Fig. 2 is a plan view of the. lower end of the spark plug and cylinder head fragment illustrated in Fig. 1 and,

Fig. 3 is a partly sectional view of a somewhat modified form of spark plug and shows a fragmentary section of a different type of cylinder head adapted toreceive the spark plug. I

Referring to the drawing in detail, the improved spark plug includes .an outer member or casing generally indicated at III, formed'of some durable material such as iron or steel. This casing is provided intermediate its length with a polygonal section l2, preferably in the form of a hexagon, to which a tool may be applied for inserting the spark plug in the cylinder head or' usually formed of some relatively soft materialsuch as aluminum or an aluminum alloy and the bushing I6 is formed of a hard and durable ma- 55 terial such as iron or steel and is screw threaded A further object resides in the provision of an improved spark plug having interchangeable into the cylinder head in such a manner as to I Q become a permanent part of the cylinder head so that the spark plug may be threaded into and out of the bushing without moving the bushing relative to the cylinder head. After it isinserted in place the bushing I6 is ordinarily machined so that its ends conform to the general contour of the adjacent portions of the cylinder head. On the side of the polygonal portion opposite the screw threads l4 the casing l0 extends as a hollow tubular member provided adjacent its upper end with external screw threads 20 adapted to receive a threaded coupling member to secure the spark plug cable to the spark plug. The casing I0 is provided with a concentric bore extending entirely therethrough and within this bore is disposed a center conductor 22 disposed substantially concentric with the bore and the easing I0, extending at its lower end somewhat below the lower end of the casing Ill and terminating at its upper end a considerable distance short of the upper end of the casing. This center conductor is insulated from the casing ill by the insulating elements 24, 26 and 28 which may be formed of any suitable dielectric material such as mica. In the arrangement illustrated the insulating'elements 24 and 28 may be made of sheets of mica arranged in' concentric cylindrical form, and the element 26 may be made of disks of mica arranged in superimposed relation. At its upper end the central conductor 22 is beaded over the flush 'upper ends of the insulating elements 24 and 26, as indicated at 30, to maintain the position of the central conductor in the spark plug against downward movement and provide a suitable contact portion for the end of a spark plug cable. The lower end of the insulating element 26 rests upon a radial shoulder 32 formed in the casing in so that the central conductor 22 is located in the spark plug. against change of position in onedirection by the length of the in-' sulating element 26 and the thickness of a rein forcing washer 34 inserted between the beaded over end of the central conductor and the upper ends of the insulating elements 24 and 26'. Pref-, erably the insulating element. 28 extends to the upper end of the casing ID to provide within this portion of the casing an insulated and shielded chamber for the connection between the spark plug cable and the central conductor 22.

At its lower end the central conductor 22 carries I the center electrode 36 which may be a disk of some suitable non-corrosive metal. The insulating element 24 extends downwardly to the upper surface of the-center electrode It and surrounding this element between the center electrode and the bottom surface of the casing Hi there is an additional insulating element 36 which may be formed in a manner similar to the insulating element 26. The element 33 by its length locates the central conductor against change of positionin an upward direction and supplements the element 23 in definitely locating the central conductor and center electrode with respect to the casing Ill.

The bushing 16 is provided at its lower end with an inwardly directed annular shoulder 40 immediately above which is an annular recess adapted to receive the annular ground electrode 42. The electrode 42 is in the form of a cylindrical member having at oneend an inwardly directed radial flange 44 of such a dimension as to provide in the end of the ground electrode a circular aperture larger than the disk-shaped center electrode 36 by an amount equal to twice the width of the spark gap 46. If desired a suitable iorm of pilot construction may be provided at the bottom of the threads (4 to maintain the exact dimension of the spark gap and suitable gaskets, not illustrated, may be applied at the ends of the ground electrode to prevent gas leakage past the spark plug.

The following are among the advantages which this improved form of spark plug presents over the forms now generally in use. The casing It, the central conductor 22, the center electrode 36 and the various insulating elements 24, 26, 26 and 33, constitute a unitary element entirely separate from the bushing I6 and the ground electrode 42. When the casing and the associated elements is removed as a unitary structure from the cylinder head, the center electrode 36 and the insulating element 36 are immediately in condition for cleaning and reconditioning without the necessity of any further separation of elements. After the casing and its associated elements has been removed from the cylinder head, the ground electrode 42 may be separately removed and, upon removal, is immediately in condition for cleaning and reconditioning. With this form 01' spark plug it is therefore apparent that it is not necessary, in order to clean and recondition the plug, to separate the plug after it has been removed from the cylinder head or to reassemble and adjust it before reinsertlng it in the cylinder head. Furthermore, by providing the ground electrode 42 as aseparate' integral unit, it becomes possible to replace this ground electrode separately to renew the spark plug without having to replace the relatively expensive portion including the casing l6 and the associatedelements. As practically all of the deterioration in .a spark plug takes place in the spark gap it the center electrode to provide a spark gap of the proper width. The ground electrode 42'is a relatively inexpensive part and by providing ground electrodes of the general form indicated in a number of proper oversizes the life of'a spark plug may be indefinitely extended. A- further advantage resides in the fact that. dissipation of heat from the spark plug is greatly facilitated by the improved constru'ctionwhich eliminates vari- I ous restrictions and obstacles which haveheretoforebeen included in spark plug construction. The ground electrode 42 may convey its heat through relatively extensive areas at its opposite ends to the shoulder 40 and the lower end of the casing l0, and heat from the center portion of the spark plug is readily transferred through the relatively extensive area of the screw thread 14 to the bushing l6, and from the bushing the heat passes through but a single screw threaded joint to reach the cylinder head l8 from which it is dissipated by the integral cooling flns 46. If gaskets are used at the ends of the ground electrode they may bemade of some good heat conducting material such as solid copper. This improved construction therefore not only provides more extensive areas for'conducting heat from the spark plug to the cylinder head but eliminates one or more breaks in the continuity of the heat flow path from the spark plug to the cooling medium. Thus it is apparent that among the various advantages of the improved spark plug construction illustrated in Figs. 1 and 2 are improved cooling of the spark plug, better facility in cleaning and reconditioning the spark plug,

and an economical manner of renewing the spark plug so that'the life of the relatively expensive portion thereof may be greatly prolonged.

The slightly modified form of spark plug shown in Fig. 3 is generally similar to the form shown in Fig. I particularly as to the casing in and the associated central conductor, center electrode and insulating elements. The ground electrode 42' is also generally similar to the ground electrode 42 of ig. 1 but is modified to the extent that it is provided with an additional inwardly directed flange 50 at the end opposite the flange 44'.- The extra flange 50 surrounds an aperture somewhat smaller than that provided by the flange 44 so that, when the diameter of the center electrode 36 is decreased by cleaning and reconditioning the ground electrode 42 may be reversed to bring the flange 50 opposite the center electrode 36 to maintain the spark gap 46 at the proper width. Fig. 3 also shows 'that the spark plug may be readily assembled into a cylinder head which is not provided with a spark plug receiving bushing. In some forms of cylinder heads, particularly those adapted for use on liquid cooled engines, the head itself may be made of a material sufliciently durable to provide the spark plug aperture, and the spark plug receiving bushing i6 may he therefore eliminated. In providing the spark plug aperture directly in the cylinder head the inwardly directed flange or screwed into theaperture until'the groundelectrode is compressed between the shoulder 46' and the lower. end of the casing; This form of spark plug contains all of the advantages mentioned I above and the additional advantage that the ground electrode, by reason of its reversible construction, while slightly more expensive willlast approximately double the life of the ground electrode illustrated in Fig. 1. A further advantage of the construction in Fig. 3 is that the heat from the'spark plug is carried directly tothe cylinder head l8 and transferred immediately to the cooling medium and there are no restrictions or obstacles in the path of the heat flow from the spark plug to the cylinder head and the cooling medium.

While an improved spark plug constructed according to this invention has been illustrated and described in two slightly modified forms for the purpose of illustrating the invention, it is to be understood that the invention is in no way limited to the particular constructional forms so illustrated and described but that such changes in the size, shape and arrangement of parts may be resorted to as come within the scope of they appended claims.

Having now described the invention so that others skilled in the art may clearly understand the same, what it is desired to secure by Letters Patent is as follows:

1. In a spark plug adapted to be inserted in an engine cylinder head, a unitary center portion including a center electrode, and a separate ground electrode adapted to be associated with said center portion by said cylinder head.

2. In a spark plug adapted to be inserted in an engine cylinder head, a unitary center portion including a center electrode, and an annular ground electrode entirely separate from said center portion adapted to be held in position surrounding said center electrode by said cylinde head.

3. In a spark plug adapted to be inserted in an engine cylinder head, a unitary center portion including a casing, a central conductor, a center electrode and an insulating body, and a ground electrode entirely separate from said center portion adapted to be retained in said cylinder head by said center portion.

4. In a spark plug adapted to be inserted in a cylinder head, a unitary center portion including a casing, a central conductor, a center electrode and a body of insulating material, and a separate ground electrode of substantally annular form adapted o be separately inserted in said cylinder head and retained therein by said center portion, said ground electrode having at one end an inwardly directed annular flange to cooperate with said center electrode to provide a spark gap.

5. In a spark plug adapted to be inserted in a cylinder head, a unitary center portion including a casing, a central conductor, a center electrode and a body of insulating material, and a separate ground electrode of substantially annular form adapted to be separtely inserted in said cylinder head and retained therein by said center portion.

said ground electrode having at each end an inwardly directed annular shoulder adapted to alternatively cooperate with said center electrode to provide a spark gap, the flange at one end of said ground electrode surrounding an aperture having a smaller diameter than the aperture surrounded by the flange at the opposite end of said ground the same in operative position relative to saidground electrode.

'7. In the combination of a cylinder head having a spark plug receiving aperture therein, and a spark plug, a separate annular ground electrode for said spark plug, a ground electrode receptacle having an inwardly directed shoulder at the inner end thereof provided in said cylinder head, a unitary center portion of said spark plug having a casing provided with a screw threaded portion, and a center electrode spaced from said casing, by substantially the length of said ground electrode, and screw threads in said aperture above said receptacle to receive said center portion and retain the same in position such that the end of said casing bears upon the adjacent end 01 said ground electrode. I

8. A two piece spark plug comprising in combination a body portion carrying a fixed center i electrode, a ground electrode separate from said body portion, and means including a ledge in a spark plug receiving aperture for releasably clamping said ground electrode in operative position with respect to said center electrode.

9. In combination a spark plug body portion carrying a center electrode, a ground electrode separatefrom said body portion, a ledge located in a spark plug receiving aperture and means for clamping said ground electrode in between said ledge and said body portion and in spaced relation to said center electrode.

10. A ground electrode for a spark plug comprising a unit separable from the spark plug body and having end portions of different diameters for selectively providing spark gaps of (litterent sizes. 7

' EDWARD HOWELL PENN. 

